The present invention features methods for the identification and development of mammalian stem cells and their derivatives. The invention also features methods for assessing the health of mammalian cells, including both stem cells and somatic cells.
Stem cells are unique cell populations that have the ability to divide (self-renew) for indefinite periods of time, and, under the right conditions or signals, to differentiate into the many different cell types that make up an organism. Stem cells derived from the inner cell mass of the blastocyst are known as embryonic stem (ES) cells. Stem cells derived from the primordial germ cells, and which normally develop into mature gametes (eggs and sperm), are known as embryonic germ (EG) cells. Both of these types of stem cells are known as pluripotent cells because of their unique ability to differentiate into derivatives of all three embryonic germ layers (endoderm, mesoderm, and ectoderm).
The pluripotent stem cells can further specialize into another type of multipotent stem cell often derived from adult tissues. Multipotent stem cells are also able to undergo self-renewal and differentiation, but unlike embryonic stem cells, are committed to give rise to cells that have a particular function. Examples of adult stem cells include hematopoietic stem cells (HSC), which can proliferate and differentiate to produce lymphoid and myeloid cell types, bone marrow-derived stem cells (BMSC), which can differentiate into adipocytes, chondrocytes, osteocytes, hepatocytes, cardiomyocytes and neurons, and neural stem cells (NSC), which can differentiate into astrocytes, neurons, and oligodendrocytes. Multipotent stem cells have also been derived from epithelial and adipose tissues and umbilical cord blood (UCB).
A considerable amount of interest has been generated in the fields of regenerative medicine and gene therapy by recent work relating to the isolation and propagation of stem cells. The ability of stem cells to be propagated indefinitely in culture combined with their ability to generate a variety of tissue types makes the therapeutic potential from these cells almost limitless.
Although stem cells, particularly embryonic stem cells have enormous clinical potential as starting points for the generation of various replacement tissue and cells, a significant limitation to their usefulness is the requirement that the stem cells must be maintained in the undifferentiated state in cell culture. Maintaining embryonic stem cells in the undifferentiated state is very challenging, even in the hands of an experienced investigator, as a significant fraction of embryonic stem cells differentiate each time they are passaged and manipulated in culture. Furthermore, the differentiation pathway, once initiated, is irreversible. Therefore, the identification of stem cells prior to the initiation of differentiation is critical for the cells to be therapeutically useful. Current methods for testing the differentiated state of an embryonic stem cell line include the use of pluriporent stem cell markers that are unable to distinguish between undifferentiated cells and cells which have entered, at least partially, the differentiation pathway.
Improved methods are needed to assess the pluripotency of stem cells, such as embryonic stem cells, both male and female, and to identify embryonic stem cells prior to the initiation of the differentiation pathway. Such methods are needed to help realize the full therapeutic potential of these cells.